Gas turbine engine with geared turbofan and oil thermal management system

ABSTRACT

A lubricant supply system for a gas turbine engine has a lubricant lube pump delivering lubricant to an outlet line. The outlet line is split into at least a hot line and into a cool line, with the hot line directed primarily to locations associated with an engine that are not intended to receive cooler lubricant, and the cool line directed through one or more heat exchangers at which lubricant is cooled. The cool line then is routed to a fan drive gear for an associated gas turbine engine. A method and apparatus are disclosed.

BACKGROUND OF THE INVENTION

This application relates to an oil system for providing oil to a gearassociated with a geared turbofan in a gas turbine engine.

Gas turbine engines are known, and typically include a fan deliveringair into a compressor section. Compressed air from the compressorsection is delivered into a combustion section, mixed with fuel, andignited. Products of this combustion pass downstream over turbine rotorswhich are driven to rotate.

A low pressure turbine rotor drives a low pressure compressor, andtraditionally has driven a fan at the same rate of speed.

More recently, a gear reduction has been included between the lowpressure turbine and the fan such that the fan and the low pressurecompressor can rotate at different speeds.

Oil management systems are known, and typically provide oil to enginebearings and other locations within the engine. As a result of gearsbeing added to turbofan engines, additional components require cooling,thereby necessitating new cooling systems and methodologies.

SUMMARY OF THE INVENTION

In a featured embodiment, a lubricant supply system for a gas turbineengine has a lubricant pump delivering lubricant to an outlet line. Theoutlet line is split into at least a hot line and a cool line, the hotline being directed primarily to locations associated with an enginethat are not intended to receive cooler lubricant. The cool line isdirected through one or more heat exchangers at which lubricant iscooled. The cool line is then routed to a fan drive gear for anassociated gas turbine engine.

In another embodiment according to the previous embodiment, a valve ispositioned on the cool line and splits the cool line into two lines,with a first line being directed through a fuel/oil cooler at which thelubricant will be cooled by fuel leading to a combustion section for thegas turbine engine. The lubricant not being directed to the fuel/oilcooler is directed to at least one other cooler through a second line.

In another embodiment according to the previous embodiment, the at leastone other cooler includes an air-to-oil cooler.

In another embodiment according to the previous embodiment, the at leastone other cooler also includes an oil-to-oil cooler at which oil from agenerator exchanges heat with the oil in the second line.

In another embodiment according to the previous embodiment, the coolline supplies lubricant to a journal bearing in a fan drive gear.

In another embodiment according to the previous embodiment, a valveselectively supplies lubricant from the hot line to the fan drive gearwhen additional lubricant is necessary.

In another embodiment according to the previous embodiment, the hot lineintermixes with a portion of the oil in the cool line prior to beingdirected to the locations associated with an engine that are notintended to receive cooler lubricant.

In another featured embodiment, a gas turbine engine has a fan, acompressor section, including a low pressure compressor section and ahigh pressure compressor section, a combustor, and a turbine sectionincluding both a low pressure turbine and a high pressure turbinesection. The low pressure turbine section drives the low pressurecompressor section, and a fan drive gear is provided such that the lowpressure turbine further drives the fan, with the fan and the lowpressure compressor being driven at different rates. A lubricant systemincludes a lubricant pump delivering lubricant to an outlet line. Theoutlet line splits into at least a hot line and a cool line, with thehot line directed primarily to locations in the gas turbine engine thatare not intended to receive cooler lubricant. The cool line is directedthrough one or more heat exchangers at which the lubricant is cooled.The cool line is then routed to the fan drive gear.

In another embodiment according to the previous embodiment, thelocations in the engine that are not intended to receive coolerlubricant include bearings associated with at least the turbine section.

In another embodiment according to the previous embodiment, a valve ispositioned on the cool line and splits the cool line into two lines,with a first line directed through a fuel/oil cooler at which the oilwill be cooled by fuel leading to a combustor. The lubricant not beingdirected to the fuel/oil cooler is directed to at least one other coolerthrough a second line.

In another embodiment according to the previous embodiment, the at leastone other cooler include an air-to-oil cooler.

In another embodiment according to the previous embodiment, the at leastone other cooler also includes an oil-to-oil cooler at which oil from agenerator exchanges heat with the oil in the second line.

In another embodiment according to the previous embodiment, the coolline supplies lubricant to a journal bearing in the fan drive gear.

In another embodiment according to the previous embodiment, a valveselectively supplies lubricant from the hot line to the fan drive gearwhen additional lubricant is necessary.

In another embodiment according to the previous embodiment, the lowpressure turbine has a pressure ratio greater than about 5:1.

In another embodiment according to the previous embodiment, a gearreduction ratio of the fan drive gear is greater than about 2.3.

In another embodiment according to the previous embodiment, a diameterof the fan is significantly larger than a diameter of the low pressurecompressor.

In another embodiment according to the previous embodiment, thelubricant in the hot line is intermixed with a portion of the lubricantfrom the cool line prior to being delivered to the locations in the gasturbine engine that are not intended to receive cooler lubricant.

In another featured embodiment, a method of managing lubricant supplyfor a gas turbine engine includes the steps of moving a lubricant from alubricant pump into an outlet line, and splitting the outlet line into acool line which is delivered into at least one heat exchanger to coolthe lubricant. The cooled lubricant is then delivered to a gearreduction that drives a fan associated with the gas turbine engine.Lubricant is delivered from a hot line which is not passed through theat least one heat exchanger to bearings associated with at least aturbine section in the gas turbine engine.

In another embodiment according to the previous embodiment, thelubricant in the hot line is intermixed with a portion of the lubricantin the cool line prior to being delivered to the bearings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a gas turbine engine.

FIG. 2 is a schematic of an oil management system for the gas turbineengine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmenter section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath B whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 (shown schematically) to drive the fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a high pressure compressor52 and high pressure turbine 54. A combustor 56 is arranged between thehigh pressure compressor 52 and the high pressure turbine 54. Amid-turbine frame 57 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 57 further supports bearing systems 38in the turbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes.

The core airflow C is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to thepreviously mentioned expansion.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle.The geared architecture 48 may be an epicycle gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.5:1. It should be understood, however, that theabove parameters are only exemplary of one embodiment of a gearedarchitecture engine and that the present invention is applicable toother gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of 1 bm of fuel being burned divided by 1 bf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tambient degR)/518.7)^0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 is an oil management system for the gas turbine engine system ofFIG. 1. The oil management system 140 is utilized in association with afuel system 143, and a variable frequency generator 160 and its oilcooling system circuit 162.

Fuel from a fuel tank 142 passes to a fuel/oil cooler 144. The fuel isheated, and cools a lubricant, as will be explained below. A main fuelpump 146 drives the fuel into further fuel lines 243 and then intonozzles 148 in a combustor, such as combustor 26 as shown in FIG. 1. Itis known in the art to heat the fuel to improve the efficiency of theoverall engine. The fuel/oil cooler 144 provides this function.

At the same time, the variable frequency generator 160 is driven byturbine rotors to generate electricity for various uses on an aircraft.As shown in oil cooling system circuit 162, the oil passes through anoil-to-oil cooler 164, and may also pass through an air-to-oil cooler 66before returning to the variable frequency generator 160.

An oil supply system 150 includes a main oil pump 70 taking oil from amain oil tank 72. The terms “oil” and “lubricant” are usedinterchangeably in this application and cover a fluid used to lubricatesurfaces subject to relative rotation. The oil is delivered through adownstream line 73, and split between two lines 74 and 75. Line 74 issent directly to line 86 without cooling. A modulating valve 76 iscontrolled to achieve a desired fuel temperature. As an example, asensor 300 may send a signal to a control regarding a sensed temperatureof the fuel downstream of the fuel oil cooler 144. The valve 76 routesthe volume of oil between line 78 and 80 to achieve the desiredtemperature of the fuel.

The oil passing to line 78 passes through the fuel/oil cooler 144 andheats the fuel. The oil is cooled before returning to a commondownstream line 82. The downstream line 82 could be called a “cool” oilline, as the oil will be cooler than the oil in “hot” line 74 which hasnot been cooled in any heat exchanger. For purposes of this application,line 75 is seen as part of the “cool” line even though the lubricant hasyet to be cooled.

The oil directed by the valve 76 into line 80 passes through anair-to-oil cooler at 68 which is exposed to air which is cooler than theoil in line 80, and which cools the oil. Downstream of the air-to-oilcooler 68, the oil passes through the oil-to-oil cooler 164, and mayactually be somewhat heated by cooling the oil for the variablefrequency generator. Still, the oil reaching line 82 downstream of theoil-to-oil cooler 164 will be significantly cooler than the oil in line74. Some of the oil in line 82 is directed into a line 84, to a journalbearing 152, and to the fan drive gears 154. Thus, cooler oil issupplied to the bearing 152 and gears 154 than is supplied from the line74. As can be seen, a line 86 branches off of the “cool” line 82 at ornear the point at which “cool” line 84 breaks away to go to the journalbearing 152 and the gears 154. A return line 88 is downstream of thejournal bearing 152 and gears 154. The lubricant in line 86 mixes withthe lubricant in “hot” line 74, but downstream of the branch line 84.

It is desirable to provide cooler oil to these locations than isnecessary to be supplied to bearings 90, or other locations associatedwith the engine. The bearings 90 as shown in FIG. 2 may equate to theseveral locations of bearings 38 as shown in FIG. 1. The journal bearing152 and the fan drive gears 154 would be part of the geared architecture48 as shown in FIG. 1.

On the other hand, cooling all of the oil associated with the enginebearings 90 would reduce the overall efficiency of the engine. Thus,splitting the oil, and cooling the oil to be directed to the bearings152 and/or gears 154 provides cooler oil to those locations, while stillallowing the hotter oil to be directed to locations that do not needcooler oil.

In addition, a valve 92 can selectively direct additional oil to thegears 154 if additional oil is necessary, such as at high power times.At other times, the valve 92 may direct lubricant through line 94 backto a return line 95 leading back to the oil tank 72.

The overall configuration thus results in an oil supply system whichdirects hotter oil to the locations which do not need cooler oil, butwhich also cools oil to be directed to areas associated with the fandrive gear.

Further details of a similar oil management system are disclosed inco-pending U.S. patent application Ser. No. 13/362,094, entitled “GasTurbine Engine With Geared Turbofan and Oil Thermal Management SystemWith Unique Heat Exchanger Structure, filed on even date herewith, andowned by the assignee of the present application.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

The invention claimed is:
 1. A lubricant supply system for a gas turbineengine comprising: a lubricant pump delivering lubricant to an outletline, said outlet line splitting into at least a hot line and into acool line, said hot line being directed primarily to locationsassociated with the engine that are not intended to receive coolerlubricant, and said cool line being directed through one or more heatexchangers at which lubricant is cooled, and said cool line then beingrouted to a fan drive gear for the associated gas turbine engine; atleast one of said one or more heat exchangers is a fuel/oil cooler atwhich the lubricant will be cooled by fuel leading to a combustionsection for the gas turbine engine, and said fuel/oil cooler beingdownstream of a point where said outlet line splits into said at leastsaid hot line and said cool line, such that said hot line is notdirected through said fuel/oil cooler; and wherein a valve is positionedon said cool line and splits said cool line into two lines, with a firstline being directed through said fuel/oil cooler and the lubricant insaid cool line not being directed to the fuel/oil cooler being directedto at least one other cooler through a second line.
 2. The system as setforth in claim 1, wherein said at least one other cooler includes anair-to-oil cooler.
 3. The system as set forth in claim 2, wherein saidat least one other cooler also includes an oil-to-oil cooler at whichoil from a generator exchanges heat with the oil in said second line. 4.The system as set forth in claim 1, wherein said cool line supplieslubricant to a journal bearing in a fan drive gear.
 5. The system as setforth in claim 1, wherein a valve selectively supplies lubricant fromsaid hot line to the fan drive gear when additional lubricant isnecessary.
 6. The system as set forth in claim 1, wherein said hot lineintermixes with a portion of the lubricant in the cool line prior tobeing directed to the locations associated with an engine that are notintended to receive cooler lubricant.
 7. A gas turbine enginecomprising: a fan, a compressor section, including a low pressurecompressor section and a high pressure compressor section; a combustor;a turbine section including both a low pressure turbine and a highpressure turbine section, and said low pressure turbine section drivingsaid low pressure compressor section, and a fan drive gear provided suchthat said low pressure turbine further driving said fan, with said fanand said low pressure compressor being driven at different rates; alubricant system including a lubricant pump delivering lubricant to anoutlet line, said outlet line splitting into at least a hot line andinto a cool line, said hot line being directed primarily to locations inthe gas turbine engine that are not intended to receive coolerlubricant, and said cool line being directed through one or more heatexchangers at which the lubricant is cooled, and said cool line thenbeing routed to said fan drive gear; at least one of said one or moreheat exchangers is a fuel/oil cooler at which the lubricant will becooled by fuel leading to a combustion section for the gas turbineengine, and said fuel/oil cooler being downstream of a point where saidoutlet line splits into said at least said hot line and said cool line,such that said hot line is not directed through said fuel/oil cooler;and wherein a valve is positioned on said cool line and splits said coolline into two lines, with a first line being directed through saidfuel/oil cooler and the lubricant in said cool line not being directedto the fuel/oil cooler being directed to at least one other coolerthrough a second line.
 8. The gas turbine engine as set forth in claim7, wherein said locations in the engine that are not intended to receivecooler lubricant include bearings associated with at least the turbinesection.
 9. The gas turbine engine as set forth in claim 7, wherein saidat least one other cooler include an air-to-oil cooler.
 10. The gasturbine engine as set forth in claim 9, wherein said at least one othercooler also includes an oil-to-oil cooler at which oil from a generatorexchanges heat with the oil in said second line.
 11. The gas turbineengine as set forth in claim 7, wherein said cool line supplieslubricant to a journal bearing in said fan drive gear.
 12. The gasturbine engine as set forth in claim 7, wherein a valve selectivelysupplies lubricant from said hot line to the fan drive gear whenadditional lubricant is necessary.
 13. The gas turbine engine as setforth in claim 7, wherein said low pressure turbine having a pressureratio greater than about 5:1.
 14. The gas turbine engine as set forth inclaim 7, wherein a gear reduction ratio of said fan drive gear isgreater than about 2.3.
 15. The gas turbine engine as set forth in claim7, wherein a diameter of said fan is significantly larger than adiameter of said low pressure compressor.
 16. The gas turbine engine asset forth in claim 7, wherein the lubricant in the hot line isintermixed with a portion of the lubricant from the cool line prior tobeing delivered to said locations in the gas turbine engine that are notintended to receive cooler lubricant.
 17. A method of managing lubricantsupply for a gas turbine engine comprising: moving a lubricant from alubricant pump into an outlet line, and splitting the outlet lines intoa cool line which is delivered into at least one heat exchanger to coolthe lubricant, and the cooled lubricant then being delivered to a gearreduction that drives a fan associated with the gas turbine engine; andsupplying lubricant from a hot line which is not passed through said atleast one heat exchanger to bearings associated with at least a turbinesection in the gas turbine engine; at least one of said one or more heatexchangers is a fuel/oil cooler and lubricant is cooled by fuel leadingto a combustion section for the gas turbine engine in said fuel/oilcooler, and said fuel/oil cooler being downstream of a point where saidoutlet line splits into said at least said hot line and said cool linesuch that said hot line is not directed through said fuel/oil cooler;positioning a valve in said cool line; and splitting said cool line intotwo lines, with directing a first line through said fuel/oil cooler anddirecting the lubricant in said cool line not being directed to thefuel/oil cooler to at least one other cooler through a second line. 18.The method as set forth in claim 17, wherein lubricant in the hot linebeing intermixed with a portion of the lubricant in the cool line priorto being delivered to said bearings.